Jefferson's descendants

Jefferson's political enemies, and some biographers,
have claimed that Jefferson had a sexual relationship with
a slave named Sally Hemming, and that the two produced children.

There is a fair chance that the issue can be settled with
DNA testing. Word is it has been, that the results have been
submitted to a journal.

The method of proof would be to compare claimed black
decendents with known white decendents. However, with the
two branches of the family now separated from one another
by seven or eight generations at least (four generations
counting from the present back to Thomas along one line, then four more
generations back down the other line to presently living people),
the problem presents special difficulties.

In principle one could compare pedigrees using the same
technique illustrated for a complicated
Okinawan family  namely, analysis
with the
kinship program.
However, across such a great distance of generations
information from standard (autosomal) DNA markers would be
so diluted it would be hard to sort from noise. It
could be done  either by testing hundreds of
RFLP markers (preferably by sequencing), or by testing
scores of people on each family branch, or by a combination.
But still it would be difficult.

Fortunately, there is an ingenious alternative. Jefferson's
Y-chromosome would not be diluted by the passage of generations.
Rather, to each offspring it is either passed intact (if the
offspring is a boy), or not passed at all (to a girl). Hence,
if Jefferson had a son from his white wife, who had a son,
who had a son ... who had a son alive today, then from that
patrilineal decendent the Y-chromosome traits are available
just as from Jefferson himself. Then, assuming that among the
decendents of Sally Hemming who may be alive today and may
be decended from Jefferson, there are some who are patrilineal,
they should also have the same Jeffersonian traits at loci
on the Y-chromosome.

Sound too easy? Well, there is at least one hitch. One
alternative to the theory that Jefferson fathered Sally
Hemming's children, is that his nephew did. If the nephew
in question was Jefferson's brother's child, then he too
would share the infamous Jeffersonian Y-chromosome, and
Y-locus tests therefore would not distinguish uncle from
nephew as possible progenitor.